1. Field of the Invention
The present invention relates generally to an electric power generation system comprising a fuel cell, and to a method of designing and operating such a fuel cell power system. More specifically, the embodiments described herein include an internal or self-regulating control of a system or device requiring a parasitic load in a fuel cell power system.
2. Description of Related Art
Electric power generation systems comprising at least one fuel cell, also know as fuel cell power systems, typically have need for control of at least one system or device that requires parasitic electric load or power. Examples of such systems or devices requiring parasitic power include, but are not limited to, coolant flow systems, a motor-driven coolant pump, circulation systems that control reactant gas circulation rates for water removal, systems for stack reactant inlet pre-humidification, centrifugal water separators, and heaters needed for maintenance of stack operating temperature when the waste heat production from the fuel cell stack cannot maintain the appropriate temperature.
The related art teaches the use of various externally added active controllers, such as electronic power control units for coolant pump motor speed control, for the control and operation of such parasitic load-demanding systems or devices. For example, electrical or mechanical thermostatic control and/or current sensors provide feedback to controllers of the motor speed of a coolant pump. Such externally-added active controllers may require on-board or external power conditioning, feedback design and control, DC-to-AC converters, variable frequency inverters, and the like.
The following patents and published patent applications disclose art related to the embodiments described in the Detailed Description of this patent application:
U.S. Pat. No. 6,835,481, issued Dec. 28, 2004, to Dickman et al, discloses a fuel cell system having partial and/or total redundancy of at least one operational component, such as a redundancy of fuel cell stacks and/or fuel processors. In some embodiments, the fuel cell system includes a plurality of fuel cell stacks adapted to deliver the same maximum rated power output as a comparative fuel cell system having only a single fuel cell stack. In some embodiments, the fuel cell system includes a plurality of fuel cell stacks adapted to deliver more than the maximum rated power output of the comparative fuel cell system. In some embodiments, the fuel cell system includes a plurality of fuel cell stacks having at least n+1 (or total) redundancy compared to a fuel cell system having only a single fuel cell stack. In some embodiments, the fuel cell system includes a control system and/or structure adapted to limit the applied load to the system.
U.S. Pat. No. 6,294,278, issued Sep. 25, 2001, to Wohr et al, discloses a fuel cell system having two fuel cell stacks with different operating temperatures, i.e. a low temperature stack (LT stack) and a high temperature stack (HT stack). The high temperature stack is connected in front of the low temperature stack with respect to the process flow of fuel through the fuel cell system.
U.S. Pat. No. 6,158,537, issued Dec. 12, 2000, to Nonobe, discloses a power supply system with a stack of fuel cells and a storage battery that includes a remaining charge monitor for measuring the remaining charge of the storage battery. The remaining charge monitor detects the remaining charge of the storage battery at the time of stopping operation of the power supply system. In case the remaining charge of the storage battery is not greater than a predetermined level, the fuel cells continuously charge the storage battery until the remaining charge reaches the predetermined level. The power supply system is stopped after the charging operation of the storage battery has been accomplished. At a next start of the power supply system, the storage battery functions as a primary power source to supply electric power to a loading until the warm-up of the fuel cells is completed.
U.S. Pat. No. 6,083,636, issued Jul. 4, 2000, to Hsu, discloses a system and method for producing electricity with a fuel cell power system. The power system includes an assembly of fuel cell stacks that operate at different temperatures, which vary between two or more of the fuel cell stacks. The fuel cell stack can have multiple temperature regions formed axially along the stack, or a plurality of spatially separated fuel cell stacks can be employed to heat a reactant from an input temperature to a desired temperature. The fuel cell stacks have operating temperatures in the range between about 20 degrees Centigrade and about 2000 degrees Centigrade.
U.S. Pat. No. 4,000,003, issued Dec. 28, 1976, to Baker et al, discloses a hybrid fuel cell secondary battery system suitable for low power sensor applications. The system comprises in combination, a fuel cell, a fully contained fuel and oxidant source for the fuel cell, a DC to DC power processor for boosting the voltage output from the fuel cell, and a nickel-cadmium battery in parallel with the output from the DC to DC processor to sustain peak power drains.
U.S. Patent Application Publication No. 2002/0072834, published Jun. 13, 2002, to Scheffler et al, discloses a method and system for controlling a fuel cell power plant in a predictive manner providing a rapid response of the fuel cell stack assembly (CSA) without creating an unacceptable condition of reactant/coolant starvation caused by instantaneous electrical load transients of the load(s) controllably connected to the CSA. A demand signal representing the anticipated current/power required by the electrical load(s) is provided. A current signal representative of the actual current drawn by the load(s) is provided. The greater of the demand signal and the current signal is selected and utilized to provide a control signal for regulating one or more of the reactants and coolant to effect the operating process of the CSA. One or more status signals indicative of the status of a regulated one or more of the reactants/coolant and/or a respective operating process effected, is provided. Each status signal is transformed to a respective load capability signal which is used to regulate load current based on fuel cell reactant status and/or CSA predicted performance during transients. The lesser of the demand signal and each of the load capability signals is selected to provide an output signal for commensurately controlling a system load.
U.S. Patent Application Publication No. 2004/0202900, published Oct. 14, 2004, to Pavio et al, discloses a system and method for controlling or otherwise effectively managing cell voltage degradation in the operation of a fuel cell device. The system comprises inter alia a fuel cell in parallel electrical connection with a secondary power source and an automated controller for switching between power supplied from the fuel cell and the secondary power source.
U.S. Patent Application Publication No. 2005/0164048, published Jul. 28, 2005, to Wheat et al., discloses a fuel cell system that includes fuel cell stacks electrically connected in parallel and supplying a gross current to a load. A controller determines the gross load current and produces a desired current through the load by adjusting, based on the gross load current, at least one parameter affecting at least one of the inputs to and outputs from the system. This system allows a stack design and its voltage output to be kept constant while stacks are added for increased power.